In the operation of a fluid system serving a plurality of work elements, the work elements often demand large volumes of fluid from their associated hydraulic fluid pump. Situations arise where the work elements demand fluid at a rate greater than the capacity of the pump, thus flow limiting occurs. In such situations, one or more of the work elements, for example, demand more fluid than they are capable of receiving, while another work element requires fluid at a very high pressure in order to continue functioning under its existing load.
In a series arrangement, the "upstream" work elements receive the needed fluid first, leaving the "downstream" elements to starve. In a parallel arrangement of work elements, the fluid follows the path of least resistance. Therefore, the elements having the lowest load pressures are supplied fluid first, leaving the work elements demanding a higher load pressure with an insufficient fluid flow.
When a work attachment is added to the fluid system for a specific vehicle application, the flow demands of the work attachment may exceed the flow capacity of the pump or pumps if the hydraulic system remains in a fixed element priority, such as described above. In this state, controllably of the work elements and/or work attachment is severely limited. Attempts by the operator to adjust his inputs correctly to avoid or overcome this state often lead to poor production. In addition, automatic functions, such as an auto dig cycle for an excavator, can not be implemented on such a machine. When flow limiting occurs during an automatic function cycle, the machine stalls or incorrectly performs the function.
The present invention is directed to overcoming one or more of the problems as set forth above.